Method of producing puffed pulp



Aug-'8, 1933 J. E. PLUMSTEAD METHOD OF PRODUCING-PUFFED PULP Filed Oct. 3, 1930 CA UST/C SOL UT/O/V FEED lunas` ppal/Maf 7L Inueni'or.

, nomical and thoroughly elicient process of treat- U tus for carrying out the method.

Patented Aug. 8, 1933 UNITED STATES PATENTToI-FICE 1,921,371 v METHOD 40E PoDU'cING PUFED PULP Joseph E. Plumstead, Wilmington, Del., assignor v to The Jessup & Moore Paper Co., Philadelphia, Pa., a, Corporation of Massachusetts Application october 3, 1930. serial N. `486,263

1s claims. (ci. ssa-1s) creased in order to obtain the same puffing action as .obtains with `the thinner yconsistency of the mass and a lesser strength of treatingcaustic alkali solution. `In the treatment of pulp with a solution of caustic soda or. caustic alkali, there 60 is to contend with the variable of the concentration or strength of the caustic soda in the treating solution, and there is also the variable of the concentration or consistency of the pulp in the mixture of pulppand caustic soda solution. As an example of what is stated above, given a 10% solutionof caustic for treating the pulp, the vtreatyment will be much more active and of greater intensity if 15 parts of pulp were used to 85parts ofv caustic solution, than if 30 parts of pulp were 7o used to '70l parts of caustic solution, the caustic solution strength in each case being 10%. That y is, for a constant strength of treating solution, the less the amount of pulp density the more intense v theaction, and the more the amount of pulp the' less-intense the action'. In order to producev a puffed pulp product having a high pulp concentration prior to the present invention, it has been necessary to use a stronger caustic solution in order to secure the properdesired puffing of the fibres when treating as a non-fluid mass. Y

The present invention makespossible the production of a high pulp concentration or consistency in the puffed, product at the completion of the process, while securing a complete and thorough pufling action without necessitating substantial increase of the strength of the caustic solution because of the non-Huid discharge, i. e. without using any greater amount of treating chemical per unit of substance treated.

In order to accomplish this according to the present invention I propose to perform the treating process with the use ofa screw press and an excess of the caustic solution above that physico- `chemically necessary to do the puiiing. The excessive solution enters the screw press Awith the pulp whereas the pulp discharged-from the screw press has a less amount of caustic solution than would be physico-chemically required for the dey sired pufng. Herein lies the economy and novelty of the present invention.

A suitable screw press is shown in Fig. 1 Vat A, and includes kneaders E and a helix B mountedin the shell C,la portion of which shell is perforated as at C so that as the wet mass is passed through the shell, it is first subjected to some, kneading actionA and then to dehydration or My present invention is an'improved method of producing puffed and purified pulp for paper making. ,l f

An object of the invention is to provide an ecoing fibrous cellulosicgmaterial to puff; swell, or curl the individual fibers thereof, so that a highly absorbent sheet of felt material may be made from the puffed pulp by a paper making machine.

Another object is to treat cellulosic fibrous pulp material in either substantially non-fluid or fluid condition in caustic solution and to simultaneously express substantially undiluted caustic solution which may be returned to the beginning of the process. Another object is to express a maximum amount of the substantially, undiluted caustic treating solution, leaving a minimum of caustic solution to be lost, consumed, or reclaimed by dilution, byremaining in the discharged puffed pulp product.

Another object is to use an excess of caustic solution above thatamount physico-chemically required to produce a certain desired puffing, curling, or purifying action upon the cellulosic fibrous pulp, and above that amount of caustic solution mechanically required to enable the mix to be kneacled and squeezed or pressed in a screw press.

Another object is to provide a process including pressing the pulp with an excess of caustic solution to cause the solution to flush the individual fibres intimately to produce a maximum desired puiilng, even with a relatively weakcaustic solution.

A further object is to provide a method for treating thesheet stock or pulp material to puff the same without the need of disintegrating the sheets or separating the individual libres and in which the sheeted pulp material may be treated in shredded or unshredded condition and inbeaten or unbeaten condition.

Other objects will appear hereinafter.

v The drawing shows diagrammatically suitable apparatus in which my method may be carried out.

Figure 1 shows a combined kneader and screw press in which my process may be carr'` Fig. 2 shows another arrangementv of appara- My experience with the puffing of pulp indicates that when a consistency or density of pulp greater than about 15' parts of pulp to 85 parts of solution is used, the caustic concentration or strength ofthe treating solution must be inpressingaction by the screw press.`

sic fibrous pulp' material in sheet or other suitable form is wetted with a caustic alkali solution. An excess of the caustic alkali solution above that amount required to physico-chemically completely pui or purify the pulp mass, is used. The wet pulp is then transferred, in either unshredded or shredded condition and in either unbeaten or beaten condition, to the screw press.

The action of the screw press and the entering excess caustic solution effects complete saturation and flushing and consequent uniform puffing of all of the bres, since its pressing action forces the caustic solution into flushing contact with each individual fibre during the expressing of the caustic solution therefrom. The expressing of the caustic solution for reuse causes a most economical caustic consumption per pound of finished material. The moist non-fluid mass of puffed purified cellulosic fibrous pulp is discharged through one opening of the screw press and the substantially undiluted expressed part of the caustic solution used is discharged through another opening of the screw press. The moisture originally present in the substantially dry fibrous cellulosic material to be treated is usually not sufiicient to substantially dilute theV caustic solution. The expressed substantially undiluted caustic solution is returned to the beginning of the process. A part of the caustic solution is consumed or used up in the processthat is, it is retained in the moist puffed pulp .and this loss or consumption is made -up by the addition of more caustic solution to the returned caustic solution at the beginning of the process.

The cellulosic fibrous pulp material may be wetted with the excess of caustic solution and then shredded or beaten or both prior to being delivered to the screwA press. It may, however, be delivered to the screw press in unshredded and unbeaten condition, but wetted with an excess of caustic and the pufliiflg will be accomplished effectively in such case also.

An important feature of the present process is that there is no necessity for prior disintegration of the pulp mass to .separate and isolate each fibre, but the massof pulp in unshredded or shredded and unbeaten or beaten condition with an excess of caustic alkali solution, may be pressed in the screw press to thoroughly distribute the caustic solution therethrough While at the same time eliminating or expressing a maximum amount of the substantially undiluted caustic solution which is returned to the beginning of the process for reuse, a minimum of caustic solution being consumed or used up in the process by passing off with the puffed pulp.

Where it is desired that the raw pulp be shredded, the process may be carried out by first lshredding the sheet pulp, that is, tearing it into bits or small sheet sections or pieces having dimensions varying between approximately onehalf inch to five inches across and having the thickness of a commercial sheet o'f pulp, wetting l der would be necessarily different from the forward speed of the mass through the screw press. Excess caustic alkali solution is used so as to provide plenty to have the desired puffing action even with a relatively weak solution, but for the screw press operation the excess may have been partly drained off.

In the screw press operation, the effect is to form a moving cylindrical wall of pulp' around the screw, through which wall the caustic solution is forced, thoroughly saturating and flushing the fibres and causing puffing of the same. This flushing of the pulp and the puiiing action is a concomitant of freeing the pulp of the caustic alkali solution, in that the solution is caused to act intimately upon the fibres of the pulp as it is being pressed through the same for its discharge.

The puffed and purified pulp product as it is delivered from the screw press is first discharged into water or washing solution so as to wash it in slush form. It is then dehydrated, and then disintegrated.prior to being made into highly absorbent paper sheets.

The excess of caustic alkali solution above that required to puff or purify the pulp is provided by as low as 70 parts of caustic alkali solution to 30 parts of raw pulp andv may be made as high as 99 parts of caustic solution to l part of cellulosic pulp to be treated. These proportions are by weight and represent the practical limits but I do not limit myself in this respect as they may be further varied.

The process may be carried out in the combination kneader and squeezer or press shown in Fig. 1 in which the raw pulp material which may be in sheet form is fed into hopper D, after having previously been shredded or not as -desired. Within the hopper D the pulp sheet frag- -ments are beaten by beater arms or blades E mounted on shaft F which also carries helix G, .beater arms H and screw press helix B. This machine may be a continuous or intermittent kneader combined in the one machine with the screw press to serve the dual purpose of kneading and mixing and also dehydrating. The puffed pulp material is discharged at K, it having been puffed during the kneading and pressing action in the machine, thorough puffing having been attained by the use of a minimum' of caustic alkali solution strength' in the treating solution although an excess of volume of the solution is used at the start of the process and during the pressing operation. This thorough puffing action with an excess volume of minimum strength caustic solution is ensured by means of the screw press which forces the caustic solution into saturating, flushing, puffing contact with each of the unisolated fibres in the non-disintegrated shredded or Whole mass of pulp. The expressed caustic solution is returned through conduit L, with interposed tank M and pump N, to the caustic solution feed at O, where more caustic solution may be added if necessary to make up the minimum loss or consumption of the caustic solution carried off by the moist puffed pulp and of a higher strength to make up for any dilution caused by moisture in the pulp and' also for loss of strength of the caustic solution due to carbonation and saponication taking place during the physico-chemical reaction of the caustic solution on the pulp.

The screw press helix is, of course, capacitated to handle pulp of concentration or consistency within certain limits depending on the design of the helix and perforated shell and the excess of caustic solution which is effective in the pulling action is the excess caustic solution remaining on the wet pulp when it is delivered to the screw press over and above that amount of caustic solution required for the helix to function properly to express the caustic solution.

While the ideal arrangement'would seem to be to have this process continuous it maybe seen that by means of a vat between the kneader and the screw section, the process may be made intermittent.

Fig. 2 shows an arrangement in which the pulp is fed to a shredder P which delivers to a kneader or mixer Q to which the caustic alkali solution is fed, the mix then being delivered to the screw press R which separates the puffed pulp and solution as before described. In this case the puffing begins inthe kneader Qk and is completed in the press R.

The strength of the treating chemical in the solution need only be about 4% although up to about 24% strength of caustic in the solution may be used in carrying out the process,lif desired. The low limit of approximately 4% is effective with a fluid concentration of 1 part of pulp to 99 parts o. caustic solution, as specified hereinbefore.

My process eiiects great saving in that it recovers substantially undiluted caustic solution by expressing the caustic solution by the same pressing action which insures completion of the desired puffing action by forcibly distributing the excess caustic solution through the pulp mass and into intimate ushing contact with each of the cellulosic fibres whether segregated or non-segregated. Only a minimum amount of the caustic solution is lost by remaining in the puffed pulp product and being washed out.

Comparative figures are submittedherewith of an example of the results of my process as cornpared with the known kneader process using the same 10% strength of caustic solution and the same 20% pulp consistency of the mix.

` Kneader process It will be noted that in the known kneader process, the entire initial charge of caustic solution remains at the finish of the puffing process and is lost, whereas by the present invention, in the example shown over 62% of the initial charge of caustic solution is recovered substantially undiluted.

Of course, examples could be drawn using any arbitrary densities or consistencies of pulp and caustic solution between the -practical limits, namely from 1% pulp and 99% caustic solution to 30% pulp and 70% caustic solutionat the start of the process.

It is understood by those skilled in the art that there are many variables affecting the degree of pufling action, among which might be named; the type of mechanicalequipment used, the character of the pulp, e. g. the percent of alphacellulose, the rate of absorption capacity of pulp, consistency or concentration of thegpulp and caustic solution mix, temperature of the pulp and caustic solutionv mix,- duration of contact between the pulp andl caustic solution.

In the examples, I have assumed to hold practically constant all variables except the type of equipment, and method of processing as specified involving the excess of solution and the pressing action.` y Y y Great saving is effected by my process even where thel proportions are so chosen that the amount of caustic solution saved is less than that remaining in the pulp at the finish. In other out departing from the scope of the invention.-

The portion of caustic discharged from the screw press in the moist pulp mass is not recoverable for immediate use in the pulp puflins process except by evaporation or fortification. However, this caustic solution so discharged from the screw press in the pulp maybe used directly, after being Washed from the pulp mass, for other chemical processes requiringa caustic solution more dilute than that required by 'the pulp pufiing process, such as cleansing or saponification, acid neutralizing operations, etc.

According to my process, there is no destruction or loss of fibre identity during they treatment. The fibre identity is not destroyed although the fibres are changed in form by being puffed and curled, whether they are separated from each other, i. e. disintegrated, or not. `My process enables the treatment `of shredded or unshredded and beaten or unbeaten sheet portions of fibrous cellulosic material.

The amount of caustic solution required to physico-chemically enter into the reaction and to completely effect the desired pufling action, cannot be stated with any degree of certainty due to the fact that it is a matter dependent upon the determined by experimentation, i. e. working back from the final product in each case todetermine what is needed. The massaction a1'- f'orded by the excess of caustic solution used in the simultaneous treating of the bres and separation of the solution from the fibres, according to the present invention, is very important.

1. The hereindescribed process of O making puffed pulpA from cellulosic fibrous material consisting in treating the fibrous cellulosic material with aA caustic solution in an amount in excess of that which is physico-chemically necessary to secure curling ofthe fibre, subjecting the wet mass in non-fluid state topressure to cause the caustic solution to fiush the fibres throughout the mass and by the same pressure to cause such part of the caustic solution to be discharged from the mass as will leave in the pulp an amount of the caustic solution less than would be physicochemically necessary for the desired pufiing.

2. A method according to claim 1 in which the pressure for effecting the fiushing action and the discharge of the caustic solution from the character of the pulp. It is a practical matter ,125

flushed mass is applied at points distributed within and throughout the mass.

3. The hereindescribed process of producing puffed pulp from cellulosic fibrous material consisting in subjecting the fibrous material to pressure in thepresence of an amount of caustic solution in excess of that physico-chemically necessary to cause usliing of the mass and curling of the fibres of the cellulosic material, said pressure being exerted at points distributed within and throughout the mass, said pressure moving said mass to a point of delivery and simultaneously with said movement of the mass discharging caustic solution therefrom, substantially as described.

4. The hereindescribed process of curling paper-felting cellulosic fibres for makingabsorbent paper consisting in subjecting the fibres to pressure in a screwfpress in the presence of caustic solution in an amount in excess of that which is physico-chemically necessary to effect curling of the fibres and of such reduced or non-mercerizing strength as would not of itself, i. e., without the said pressure and without the said excess amount, perform the desired curling action.

5. The process of claim 4 in which said excess is, say as high, by weight, as 99 parts of caustic solution to 1 part of fibres to be treated, and as low as 70 parts of caustic solution to 30 parts of fibres.

6., The process of claim 3 in which said fibrous material is subjected to said pressure in a screw press.

'7. The hereindescribed process consisting in shredding fibrous cellulosic pulp without distintegrating the pulp into individual fibres, treati" ing the shredded fibrous cellulosic pulp with a caustic solution in an amount in excess of that which is physico-chemically necessary to secure curling, puffing and purification of the fibres, and pressing the wet mass by a screw pressing action causing the solution to permeate and react to complete the desired purification and puffing of the whole mass of pulp, and by the same screw pressing action discharging a part of the caustic solution from the mass without substantial dilution, and recovering said part of the caustic solution so discharged by the pressing action.

8. The hereindescribed process consisting in taking fibrous cellulose pulp in sheet form and shredding the pulp without disintegrating the pulp into individual fibres, treating the shredded fibrous cellulosic pulp with a caustic solution in an vamount; in cexcess of that which is physicochemically necessary to secure curling, puffing and purification of the fibres, beating the pulp during the treatment with the caustic solution, and pressing the wet mass by a screw pressing action causing the solution to permeate and react to complete the desired purification and puffing of the whole mass of pulp, and bythe same screw pressing action discharging a part of the caustic solution from the mass without substantial dilution, and recovering said part of the caustic solution so discharged by the pressing action.

9. The hereindescribed method of simultaneously effecting physico-chemical treatment of 1ibrous material and separation of the treating fluid from the brous mass consisting in subjecting the saturated mass to screw pressure to cause treating fiuid to flush said mass and to be discharged therefrom, said iibrous material being shredded and beaten prior to the physico-chemical treatment.

10. The hereindescribed process of curling paper-felting cellulosic fibres for making absorbent paper consisting in subjecting the fibres to the action of caustic solution in an amount in excess of that physico-chemically necessary to ef- 100 fect said curling, subjecting the mass, together with the solution, to pressure, thereby causing the caustic solution to ush the fibres, said pressure causing discharge of caustic solution from the mass of fibres and leaving the treated mass with a caustic solution content in amount less than that which would be physico-chemically necessary to perform the desired curling.

-ll. A process according to claim 10 in which the pressure is exerted upon the fibres in a screw press and the discharge of the caustic solution takes place at different points along said screw press.

l2. The hereindescribed process of curling paper-felting cellulosic fibres for making absorbent paper consisting in flushing the fibres with caustic solution under pressure and discharging caustic solution from the mass of flushed fibres while under said fiushing pressure, leaving in said mass caustic solution in an amount less than that which would be physico-chemically necessary to perform the desired curling.

13. A process according to claim 12 in which the pressure upon the fibres and the caustic solution is exerted in a screw press and from which the discharge of the caustic solution takes place at points along said press, substantially as described.

JOSEPH E. PLUMSTEAD. 

